The development of improved techniques to interconnect and deliver optical power and signals in optical fiber systems is of growing importance as optical fiber technologies spread to various telecommunications, networking, industrial and medical applications. A unique characteristic of fiber-based transmission media is that considerable care must be taken in handling fiber optic cables because of the potential to damage the internal glass optical fiber. Unlike most electrical cables, which can be sharply bent or subjected to significant forces without impacting their performance characteristics, fiber optic cables are readily damaged under small shear forces and must maintain greater than a minimum bend radius. Sharp bends result in increased insertion loss, stress birefringence and ultimately fiber failure. In addition, the interface between the polished fiber optic connector and cable is susceptible to damage arising from the concentration of stress at the point the cable enters the connector body.
The preparation of fiber optic patchcords requires the use of a polishing process which adds cost relative to electronic cabling. Optical fiber cables can not be readily cut to length in the field, nor can they be folded to take up excess length. Optical connectors are also highly susceptible to contamination or scratching. This damage results in potential data corruption or complete loss of data transmission. Therefore, techniques and cable designs to mitigate damage to fiber optic cables address an important problem.
Various fiber optic cable designs have been disclosed that armor and isolate the delicate optical fiber from damage. For example, U.S. Pat. No. 6,233,384 by Sowell et al. discloses a crush, kink and torque resistant flexible fiber optic cable having a spiraled, rigid, metal wire layer circumferentially disposed around the cable. The prior art has also disclosed optical fibers with shape memory activated by the application of heat to the cable, for example, as in Japan Patent Application JP2000338373. In this disclosure, a shape memory alloy ribbon is coated on the outside of the optical fiber, which can spring into a predetermined shape by application of heat. In the art of suspended optical fiber cables, it is common practice to spiral optical fiber elements about a metallic “tension member” which supports the cable to prevent the optical fibers from being tensioned excessively. Such tension members are typically braided wire, which do not have appropriate mechanical characteristics to enable the cable to retain a shape.
Japanese patent JP59187303 describes an optical fiber which is plated or evaporated with a thin metal layer to retain a bend. However, this approach does not provide a means of limiting the bend radius in the bent state. An alternate approach to mechanically support a fiber optic bundle and retain its shape is described in U.S. Pat. No. 5,879,075 by Conner et al. This segmented, metallic gooseneck design is used for large diameter fiber bundles. These factors make such a cable impractical for most applications, which require a solution that satisfies multiple requirements including low cost, light weight and small form factor.